Drinking water has become one of the most important commodities in the twenty-first century. Yet sometimes significant water losses occur in water distribution networks.
The conservation of this commodity represents a considerable challenge in terms of leakage detection and leakage location in water networks. The use of mass balancing to detect water losses, wherein all of the supply volumes and particularly the water withdrawal volumes of all individual water consumers are measured, exceeds the limits of feasibility in terms of expense. Moreover, legislation requires time-based consumption measurements and consumption records for all customer data.
In order to detect leakages in water networks, conventional methods simply measure the entire water volume which flows into the network at a specific time, e.g. the time period between 02:00 and 04:00 at night. These values generate a time series that is analyzed for the presence of a sudden rise in the consumption and hence a possible leakage. Conventional methods do not allow the withdrawals from the system to be balanced. Rule-of-thumb formulas are available for determining typical water consumption of specific consumers. However, these are very general and do not allow exceptional effects, particularly those of limited duration, to be taken into consideration with sufficient accuracy.
Most water supply networks are very large and are usually divided into water supply zones. These zones are again divided into subzones, which are known as district meter areas (DMA) due to the influence of British engineers. The DMAs are so designed as to have only one inflow, whose through-flow is measured. Irregularities in water consumption and hence leakages are deduced from the observation of this through-flow measurement. According to conventional methods, provision is specifically made for performing a so-called ‘Night Flow Analysis’. In this context, a detailed record of the nightly inflow values into a DMA (e.g. every 5 seconds between 02:00-04:00 hours) is used to determine a minimal inflow value, also referred to here as background consumption, comprising the normal nightly (minimal) consumption and any existing leakages (including small leakages in particular).
A time series over days and weeks is then produced based on these minimal inflow values into a DMA during low-consumption nighttimes, e.g. between 02:00 and 04:00 hours, wherein only one value per night is provided. Any rise (particularly a sudden rise) in these minimal consumption values, said rise being detected e.g. when a threshold is exceeded, may be caused by a new leakage.
For the purpose of localization or leakage location, a step test is usually performed. For this, small regions are successively disconnected from the DMA at times of low consumption, and the change in consumption is observed. Regions resulting in a significant and inexplicable decrease in the consumption are then examined further for leakages.
Alternatively, the water system can be monitored locally for leakages by means of noise meters, and the leakage point can be calculated by observing the noise correlation.
Neither of the conventional methods cited above are suitable for continuous monitoring. Step tests are associated with considerable expense because the affected households must be notified before the disconnection and a replacement supply must be provided. Noise measurement involves considerable expense because the measurements can only be performed by specialists on site. In addition, these examinations are only possible locally. Furthermore, both conventional methods can only be used at times of low consumption, in order to avoid excessive measurement interference due to consumption fluctuations. Current methods for leakage detection therefore suffer from a fundamental problem that false alarms are reported very frequently and that a leakage is therefore erroneously assumed to be present (type 2 error). The expenses associated with localization of the leakage (sending out a search unit, acoustic localization, step test, through to excavation and drilling) are incurred in vain in such cases. This is costly and represents a nuisance to those involved.